Butadiene production



Dec. 18, 1945. 1 R. .1 PATTERSON- BUTADIENE PRODUCTION Filed Jan. 11, 1945 A TT ORNEYS mental Dee. 18,1945

BUTADIENE PRODUCTION Robert J. Patterson, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application January 11, 1943, Serial No. 472,043

1 Claim.

This invention relates to the production of butadiene by dehydrogenation of normal butane, normal butene or mixtures of normal butane and normal butene. More particularly, it relates to a method of preventing the undesirable accumulation of isobutylene in the feed due to the conventional recycle of unconverted or only partially converted C4 hydrocarbons, and at the same time increasing the utilization of the original feed and the overall yield of butadiene based on the charge.

It is now well known that in the dehydrogenation of normal butane and butenes to butadiene, substantial amounts of isobutylene are formed as by-products and build up to an objectionable extent by the recycle of the C4 hydrocarbons other than butadiene contained in the eflluent. It has been proposed to prevent this objection` able building up of isobutylene in the system by removing isobutylene from the recycled C4 hydrocarbons, namely butane and butene. One method is to effect this removal by selective absorption or selective polymerization of the isobutylene by sulfuric acid. Another 'method is to subject a portion of the recycle stream to nondestructive hydrogenation to convert the butenes to butanes, fractionate the resulting butane mixture to separate the normal butane from the isobutane, and recycle the normal butane to the dehydrogenation step. The latter method is specincally disclosed in the copending application of J. P. Jones, Serial No. 404,420, filed July 28, 1941. These procedures are not entirely satis- A factory because C4 hydrocarbon material isthereby lost from the systemreducing the overall yield of butadiene based o n the charge.

The principal object of the present invention is to provide animproved method of` making butadiene by the dehydrogenation of normal butanevor butene. Another object is to provide such a method wherein the accumulation of isobutylene as a result of the recycle is prevented. Still another object is to improve the yieldof butadiene based on the original charge. Yet another object is to effect conversion of isobutylene which would normally be recycled into normal butene which is recycled instead. Numerous other objects will hereinafter appear.

The accompanying drawing portrays diagrammatically one arrangement of equipment. whichmay be used in carrying out the process of the present invention.

In accordance with my invention the isobutylene formed in the dehydrogenation of normal butane or butene is isomerized to normal butene or butenes in manner known per se and the normal butene or butenes so formed is returned to the charge tothe dehydrogenation step.

In one embodiment, my invention may be practiced by passing the recycle -stream containing (Cl. 26o- 680) small amounts of isobutylene to a separation zone where the isobutylene is separated from the normal butane or butene or mixture of normal butane and butene 'as by fractionation. The normal butane or butene is recycled to the dehydrogenation step. The isobutylene is passed through a thermal or catalytic isomerization zone where it is subjected to known conditions of treatment effecting conversion of a substantial proportion of the isobutylene to normal butene or butenes. The isomerization eiiluent may then be fractionated or otherwise treated to segregate the unchanged isobutylene from the normal butene. The Vunchanged, isobutylene so separated may then be conveniently recycled to the isomerization step for further conversion. AThe normal butene or butenes derived vfrom the isomerization eiiluent are passed to the dehydrogenation process in which the butadiene is formed.

In the somerization step, any of the known methods of isomerizing isobutyleneto lnormal butenes may be used, such as those set forth on pages 58 and 59 of Egloif et' al., Isomerization of pure hydrocarbons, 1942; in the copendng application of Hillyer et al., Serial No. 427,830,

. filed January 22, 1942; in the paper of Egloif et al., J. A. C. S. 61, 3571-3580 (1939); in British Patent 496,676 and in U. S. Patents 2,216,284,

32,216,285, 2,217,252, 2,220,693 and 2,277,650. I

prefer to operate under conditions such that isobutylene conversion to normal butene or butenes per pass is at least 30% and preferably 40% or 50% or higher, so 'that the butene content of perature, so that the higher temperatures, namely 300 C. or above, are preferred in order to favor a high conversion to normal butenes. equilibrium concentrations of normal butene present in the equilibrium mixture with isobutylene at various temperatures are listed as follows:

Temperstnre,0.

It is preferred to so operate that the butenes contained in the isomerization effluent comprise l at least 50 per cent of normal. butene. The se- Typical y assesses A other undesirable side reactions.

cluding catalyst, temperature, pressure and contact time, to effect the desired conversion in satisfactory yields is a matter well within the present-day skill of the art and need not be set forth in detail. It may be said, however, that frequently it is preferred to use a catalyst of phosphoric acid on a suitable adsorbent carrier. Furthermore, it is preferred to use conditions minimizing or preventing polymerization, `cracking orv Referring to the accompanying drawing, a feed comprising or consisting essentially of normal butane or normal butenea'or a mixture of normal butane and at least one normal butene is introduced to the system via line I and passes through catalytic dehydrogenation unit 2 where a substantial proportion of butadiene is formed from the components ofthe feed.

Dehydrogenation unit 2 is not described in ldetail but may be of any known type, either single Vstage-or, more usually, two-stage with or without intermediate treatment for concentration of bu' tenes for feed to thesecond stage. Usually the L first'stage is so operated that the principal conversion is that of normal butene to normal butene, no or very little butadiene being formed in that step, and the butene-1 and butene-2 contained in the effluent are separated from other components and employed as feed to the second stage where the predominating reaction is conversion of normal butene to butadiene, although concomitant formation of small amounts of isobutylene and normal butane in the second stage is usually encountered.

Accordingly, construction and operation of dehydrogenation unit 2 are now well within the skill of the art. It will further be understood that while it is illustrated diagrammatically, the' recycle need not be to the original feed stream Where that is, as usual, normal butane, but that recycle of normal butane and f normal butene is usually to the first and second stages respectively.

The dehydrogenation effluent from the nal stage passes via line 3 to butadiene' separation unit 4 which is indicated diagrammatically and may be of any suitable type, employing known methods of selectively extracting butadiene, such as selective solvent extraction as by extractive distillation with furfural as a. solvent, sulfone formation, azeotropic distillation,` formation of cuprous chloride-butadiene complex, etc.

'I'he butadiene-free stream leaves via line 5 and may pass thence via line 6 to is'obutylene separation whe're isobutylene is separated or concentrated in any suitable manner, as for example by fractional distillation, solvent extraction, azeotropic distillation, sulfuric acid extraction followed by desorption, selective polymerization followed by depolymerization, etc. Unit 1 is in- Ydicated only diagrammatically because its construction and operation are well within the skill of the art. The butane leaves unit 1 via. line 8 Alo and is recycled via-line 9. Usually this is mainly normal butane, no oronly very little isobutane being formed in the dehydrogenation.v Desiracontent of the feed to unit 1 is removed in admixture with the butane.

The isobutylene, either substantially pure or in admixture with some or all of the butene-l if desired,.leaves unit 'I via line IIJ and passes tov isomerizer II where the isobutylene is converted to normal butene, usually mainly butene-2.

If desired, under appropriate circumstances, the etlluent from butadiene separation unitl 5 may partially or entirely by-pass the isobutylene separation unit I by means of line I2.

The effluent from isomerization unit II passes via line I3 forrecycle to the dehydrogenation unit 2. Usually the conversion of isobutylene to normal butene by isomerization in unit I I will be sumciently extensive to keep the isobutylene in the system from pyramiding to an objectionable.

'extent even where the entire eiliuent from isomerizer Il is recycled to unit 2 without separation of lunconverted isobutylene contained therein. i

If desired, however, the effluent from isomerizer If desired, fractionator I5 may be partially or completely by-passed by means of line I3 depending upon the operating conditions encountered.

In an embodiment vwhich is frequently prefel-red, the isobutylene separation may include the steps of treating the mixture of butene-1 and isobutylene, which is extremely difiicult to resolve by ordinary fractional distillation, in such manner as to isomerize the butene-1 to butene-2 and then fractionating this isomerizatio'n effluent to separate the butene-2 so formed from isobutylene and unconverted butene-l. This insures substantially complete absence of butene-1 from the feed to unit Il.

cation may be practiced as illustrated in the drawing by passing the mixture of isobutylene and butene-1 leaving unit 'I via line line I0 through line I8 to isomerization unit I9. The isomerization eiliuent leaving unit I9 is passed via line 20 to fractionation unit 2l which separates a fraction of butene-2 withdrawn via line 22 and a fraction of isobutylene nearly free from butene-1 withdrawn via line 23 and fed there- 50 by to isomerization unit II. A similar step for isomerization of butene-l to butene-2 may be employed in conjunction with fractionator I5 in order to facilitate separation of al1 normal butene from isobutylene in said fractionator.

It will be understood that while the drawing shows the recycle as asingle stream passing via line s into unit 2, in practice'where two-stage dehydrogenation of normal butane isl involved, y the recycle may be by Way of two streams one being normal butane to the first stage and the other being normal butene recycled to the second stage, these being separated in any manner from one another. It will also be understood that the rst stage eiiluent is most conveniently treated t0 separate a normal butene' feed which bly the normal butenes, or at least the butene-2 II maybe passed via line I4 into fractionator' Such a modiis fed to the second stage and a normal butane recycle stream which is recycled to the 'irst stage. Furthermore, while the drawing shows unit 1 ,after unit 4, their position may be interchanged, or their functions combined into a single unit in which isobutylene, butadiene, normal butane and normal'butene areseparatedfrom one another in any suitable manner.

I claim:

The` process of making butadiene which comprises catalytically dehydrogenating an aliphatic C4 hydrocarbon selected from the group consisting of normal butane and normal butenes under conditions such as to produce butadiene, separating butadiene from the dehydrogenation efiiuent, separating a fraction of isobutylene and butene-l in admixture from the dehydrogenation eluent, recycling the` butene-2 content of dehydrogenation emuent to the dehydrogenation step, treating said fraction of isobutylene and butene-l in such manner as to isomerize said butene-l to butene-Z, fractionally distilling the isomerization eiiluent to separate the butene-Z so produced from the isobutylene which is thus rendered substantially free from butene-l, treating the resulting isobutyiene in such manner as to partially isomerize it to normal butene comprising a major proportion ofJ butene-2, fractionally distilling the last-named isomerization eilluent to separate it into a fraction' containing the unconverted isobutylene and a fraction of butene-2, recycling said fraction of unconverted isobutylene to the last-named isomerization step, and feeding said last-named fraction of butene-2 to the 'dehydrogenation step.

' ROBERT J. PATTERSON. 

